A silicon microstrip sensor for use in dental digital

radiographyP.F. van der Stelt

Academic Centre for Dentistry Amsterdam, Amsterdam, the Netherlands

F.A. Triantis - University of Ioannina, Ioannina, Greece R.D. Speller - University College London, London, United

KingdomG. Hall, G.M. Iles - Imperial College, London, United Kingdom

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Introduction

• Many medical imaging procedures are now digital

• Main requirements are:– size large enough to cover the ROI – resolution diagnostically adequate– patient dose clinically acceptable

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Solid state sensor systems

• pixel sensors– high event rate capability– high overhead requirement

• strip sensors– simpler readout structures– event rate limiting ambiguities

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Aim

To develop and evaluate a new sensor using

silicon microstrip technology for 2-D medical and dental

radiographic imaging

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Technology

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data acquisition electronicsdata acquisition electronicsdata acquisition electronicsdata acquisition electronics front-end front-end electronicselectronics

front-end front-end electronicselectronics

• metal “strips” embedded in silicon• perpendicular on both sides of the chip• photons produce secondary electrons• electrical charge is depleted by the strips

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Technology

microstrips

photon

photon

electrons

silicon

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SMS technology

• photon counting characteristics (different from conventional, integrating sensors)

• enabling dual energy techniques• possibility of increased resolution

by weighed read-out of adjacent strips

• using existing chips

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Results of Monte Carlo simulation

• detection efficiency is sufficient for dental applications when a 300 µm sensor is used;

• pixel counts of <1000 can provide good image quality;

• even at 200 counts per pixel, high contrast details of 300 µm are detectable.

Speller et al. Nucl Instr and Meth A 457 (2001) 359

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Prototype silicon microstrip detector

• 300 µm double-sided silicon sensor (SINTEF, Oslo, Norway)

• p-side 427 strips on a 50 µm pitch • n-side 128 strips on an 80µm pitch• effective area 2.185 x 1.024 cm2

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Prototype (cont’d)

• four APV chips (each 128 channels) with pitch adaptor to read out the p-side (427 strips)

• one APV chip with pitch adapter to read out the n-side (128 strips)

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P-side

427 strips, 4 APV’s (2 bonded at this time)

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N-side

128 strips, 1 APV

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Hybrid architecture

Signal

Conditioning5x APV output

Sensor APV 0

APV 4APV 3APV 2APV 1

Hybrid

Clock and TriggerSlow Control

VME Crate

SEQSI

I2C

RIO2

FED

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Data procssing and image correction

• gain variation of individual strips corrected for by subtraction of factor obtained from flat field image;

• pixels in dead strips were assigned average of pixels on either side;

• different aspect ratio of pixels corrected by using each pixel 2 times along the 80 µm and 3 times along the 50 µm direction.

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Imaging results

Test images of “real” dental objects to determine the physical and diagnostic image quality

– molar – incisor– jaw section

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Image preprocessing

Raw data

Removing non-uniformities by flat field subtraction

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Image preprocessing

Dead-strip correction

Aspect ratio correction

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First images

Molar• enamel• dentine• root canal

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First images

Incisor• enamel• dentine• root canal• restoration• crack in enamel

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First images

Jaw segment• tooth structures• tooth ligament• bone architecture

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Conclusion

2-D silicon microstrip technology is a promising technology for building imaging sensors for use in dental radiography.

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Future work

• Improvement of read-out electronics

• Dose measurements (in addition to the theoretical calculations)

• Reduction in sensor size

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AcknowledgementThis project has been funded by the European

Commission under the Biomed-2 scheme, contract no. BMH4-CT96-1119,

“Biomedical Radiography and Radioscopy using Silicon Microstrip Sensors”

(BRSMS)